Struggling to market and sell a useful physical product invention

I invented and (preliminary) patented a device that makes it easier to take care of houseplants: PlantDoc. It simply changes colors depending on whether your plant's soil is wet or dry. There are some other products that do this as well (Sustee and Wrox), but both are more complicated, are less helpful, and my item is completely biodegradable and, if I ever get the demand and capacity, can be created for less than $0.25. Even with working 3 jobs and having nothing more than my garage and the extra money I set aside from my real jobs, I can make about 400 of these a day for less than $2 a piece, and I sell them for $5. It's not big money, but it's a great product that really helps keep plants looking great. I also know I can sell them, because whenever I have an opportunity to present them in-person, I have about a 75% success rate in having that person buy it. The problem is that I need to mostly sell these online, and although I think I have good visuals, I'm out of my element with digital marketing, and I don't have enough money to really invest in that. I'm hoping to eventually offer different designs, but I think the biggest market for these are as an impulse buy at garden centers, plant stores, etc. I can sell them in-person, but to really get some product sales I know I'll need to figure out a way to sell them with a simple display. Does anyone have any thoughts or advice for how to take these baby steps on a shoe-string budget and without a lot of extra time to throw at it? I'd love to hear examples or connect with anyone who can help. Also, I know our e-commerce site likely needs some fine-tuning, so any suggestions on that end are really helpful. Thank you all!